Question:

If your application or expert uses designtime information, you have to replace
uses DsgnIntf;
with
uses DesignIntf, DesignEditors;
But then you will run into an error message 'Cannot find unit Proxies.pas'

Answer:

The solution is to add DesignIde.dcp to your list of required packages.

You will have to ensure that the run-time package does not require the design-time package(s). This change in Delphi 6 enforces Borland's licence restrictions on designtime editors more strongly, which have been in the license documents since Delphi 3, I believe.

http://bdn.borland.com/article/0,1410,27717,0.html